1. Field of the Invention
The present invention relates to the field of display technology, and in particular to an active matrix organic light-emitting diode (AMOLED) IR drop compensation system and method.
2. The Related Arts
Organic light emitting diode (OLED) display devices have various advantages, including being self-luminous, low driving voltage, high luminous efficiency, short response time, high resolution and contrast, approximately 180 degree view angle, wide operation temperature range, and being capable of flexible displaying and large-area full-color displaying, and is thus considered one of the display devices that have the most prosperous future.
The OLED display devices can be classified in two types, which are passive matrix OLED (PMOLED) and active matrix OLED (AMOLED), namely direct addressing and thin-film transistor (TFT) matrix addressing, according to how it is driven. The AMOLED comprises pixels arranged in an array and is a type that actively displays, having high luminous efficiency, and is commonly used in high-definition large-sized display devices. The light emission units of the AMOLED are each independently controlled through TFT addressing. The light emission unit and the TFT addressing circuit collectively form a pixel structure that is driven by being loaded with a direct-current source voltage (OVDD) through a power signal line.
FIG. 1 is a schematic view illustrating a structure of a large-sized AMOLED display device. The AMOLED display device comprises a display panel 1, a power line L for transmission of a source voltage OVDD, an Xboard 3, and a flexible printed circuit (FPC) 4. As shown in FIG. 2, pixel driving circuits associated with n pixels are connected, one by one, to the power line L that transmits the source voltage OVDD, where n is a positive integer greater than one, and each of the pixel driving circuits comprises a typical 2T1C structure, which comprises a switch thin-film transistor T1, a driving thin-film transistor T2, a storage capacitor C, and an organic light-emitting diode D. In an ideal condition, the impedance of the power line L for the transmission of the source voltage OVDD can be neglected, meaning no IR drop occurs during the transmission of the source voltage VODD and the electrical current I that flows through each pixel driving circuit is identical in the display of a pure color and consequently, the brightness of the OLEDs of all areas should be identical, providing excellent homogeneity.
However, as shown in FIG. 3, in an actual condition, there is inevitably impedance existing along the power line L for transmission of the source voltage OVDD and IR drop is induced by the source voltage VODD transmitted along the power line L. With the sizes of the AMOLED display panels getting larger and the resolution becoming greater, the length of the power line L is increased and the impedance increased. Reference being had to FIG. 1, the level of the source voltage at location that is close to the FPC 4 and thus the site where the power is fed in is higher than that at a location distant from the site where the power is fed in.
Under the assumption that the impedance of the power line L associated with the ith pixel driving circuit is Ri, where i=1, 2, 3, . . . , n, and the electrical current flowing through the ith pixel driving circuit is Ii, the level of source voltage associated with the ith pixel is OVDDi, which can be calculated with the following formula:OVDDi=OVDDi−1−(Σm=im=nIm)Ri 
Following the direction in which the electrical current flows, the voltage division resulting from impedance of the power line L is greater at a location that is more rearward. Eventually, the source voltage OVDDi applied to the OLED is decreased with the sequence of arrangement of the n pixels. In displaying a pure color, since the electrical current Ii that flows through the ith pixel driving circuit is related to the source voltage OVDDi, different pixels have different outputs of electrical current, leading to different levels of brightness at different areas of a display panel so that the image homogeneity is poor and the displayed image quality is affected.